SEARCH · Search PubMed
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Entomopathogenic steinemematid and heterorhabditid nematodes are increasingly used to control insect pests of economically important crops. Laboratory and field simulation trials show that ticks are also susceptible to these nematodes. The authors review the potential of entomogenous nematodes for the control of ticks.
Heartwater, caused by the rickettsial organism Cowdria ruminantium, is a serious constraint to livestock development in much of sub-Saharan Africa. Traditionally, the disease has been controlled by the use of chemical acaricides to control the vector tick. The University of Florida/USAID-supported heartwater research project (based in Zimbabwe) is developing a new inactivated vaccine to control the disease. In order that the vaccine is used effectively, the project has been studying the epidemiology of the disease in different livestock production systems of Zimbabwe, and evaluating the economic impact of the disease and of its future control using a vaccine such as the one under development. Initially, field studies were conducted to characterise the communal and commercial livestock-productions systems at risk from heartwater and to understand the epidemiology of the disease. The data from these studies were then applied to an infection-dynamics model of heartwater, which was used to provide estimates of disease incidence and impact under various scenarios over a period of 10 yr. Two principal outputs of the epidemiological model (cumulative annual heartwater incidence and infection-fatality proportion) were key inputs into an economics model. The estimated total annual national losses amount to Z$ 61.3 million (US$ 5.6 million) in discounted value terms over 10 yr. Annual economic losses per animal in the commercial production system (Z$ 56 discounted values) are 25 times greater than the losses in the communal system (Z$ 2.2). The greatest component of economic loss is acaricide cost (76%), followed by milk loss (18%) and treatment cost (5%). Losses in outputs other than milk (beef, traction and manure) appear to be minimal. A new vaccine has the promise of a benefit: cost ratio of about 2.4:1 in the communal and 7.6:1 in the commercial system. A control strategy based on a new vaccine would yield additional non-financial benefits to farmers and the government resulting from reductions in the use of chemical acaricides.
The responses of adult Amblyomma variegatum ticks released from various distances to different doses of the synthetic attraction-aggregation-attachment pheromone (AAAP) (made up of orthonitrophenol, methyl salicylate and nonanoic acid in paraffin oil), dispensed from the center of circular field plots, were studied in the presence or absence of elevated levels of CO2. Up to 90% of the ticks released were attracted to the pheromone source in the presence of CO2 within 3h. CO2 alone was unattractive, similar to previous findings in Zimbabwe, but unlike results from a Caribbean A. variegatum population, which was significantly attracted to this signal. In the absence of CO2, smaller but significant proportions of the released ticks were attracted to the pheromone, albeit more slowly, suggesting another variation in the responses of this bont tick to inter- and intra-specific signals. Our results are interpreted in the light of a study undertaken elsewhere demonstrating relatively high heterozygosity among tick populations. Possible directions of further research to explore the use of the pheromone in off-host control of the tick are also highlighted.
In a study to develop anti-tick pastures, the climbing behaviour of Rhipicephalus appendiculatus on Melinis minutiflora (molasses grass) was investigated. Experiments were done with cut green stems of grass, grass dried in the shade, grass dried in sunshine, grass washed in solvent and grass growing in a study plot. In all cases a common pasture grass, Pennisetum clandestinum (Kikuyu grass), was used as control. All instars of the tick avoided climbing on the green M. minutiflora whereas most larvae, nymphs and adults climbed on the control green P. clandestinum grass. More ticks climbed on the stems dried in the sunshine than on air-dried grass. Acetone was found to be the best of 5 solvents used to extract the tick-repellent substance. Possibilities of using M. minutiflora as part of an integrated tick control package are discussed.
Beauveria bassiana is one of the most promising agents for use as a bioacaricide to control the cattle tick Boophilus microplus, responsible for economic losses and transmission of infectious diseases. With the aim of optimizing the efficacy of chemical products, as well as the use of entomopathogens, the objective of the present study was to evaluate the compatibility and the synergism between this fungus and the drug deltamethrin on a strain of B. microplus that is resistant to this product.
Control of major livestock diseases in the tropics, such as theileriosis or trypanosomosis, is still largely based on the control of their vectors. Understanding the distribution of vectors, such as ticks and tsetse flies, is needed in order to improve the efficiency and economical viability of control operations. Technical improvements such as remote sensing and global information systems have allowed valuable improvements for the prediction of large-scale vector distribution (continental to national), but trying to make these predictions at the scale of a landscape is facing other challenges. At this scale, an analysis of host/vector interactions with an evolutionary point of view is useful. A study was undertaken on a mixed game/cattle ranch in Zimbabwe during which we monitored variations in the abundance and spatial distribution of the immature free stages of Rhipicephalus appendiculatus/R. zambeziensis and R. e. evertsi, two major groups of tick species in Southern Africa. We found two contrasting distributions in relation to contact between tick larvae. The ungulate-host R. e. evertsi appeared to be unpredictable, whereas R. appendiculatus/R. zambeziensis were predictable in time and space, but associated with key-resources for ungulates (water and forage resources). The consequences of such distributions are discussed in terms of vector control.
Deer support high tick intensities, perpetuating tick populations, but they do not support tick-borne pathogen transmission, so are dilution hosts. We test the hypothesis that absence of deer (loss of a dilution host) will result in either an increase or a reduction in tick density, and that the outcome is scale dependent. We use a complementary methodological approach starting with meta-analysis, followed up by a field experiment. Meta-analysis indicated that larger deer exclosures reduce questing (host-seeking) tick density, but as the exclosure becomes smaller (<2.5 ha) the questing tick density is increased (amplified). To determine the consequences for tick-borne pathogen transmission we carried out a field experiment, comparing the intensity of ticks that fed on hosts competent for tickborne pathogen transmission (rodents) in two small (<1 ha) deer exclosures and their replicated controls. Intensity of larval ticks on rodents was not significantly different between treatments, but nymph intensity, the tick stage responsible for tick-borne encephalitis (TBE) transmission, was higher in deer exclosures. TBE seropositive rodents were found in a deer exclosure but not in the controls. We propose that localized absence of deer (loss of a dilution host) increases tick feeding on rodents, leading to the potential for tick-borne disease hotspots.
Subolesin was recently shown by both gene silencing and immunization with the recombinant protein to protect against tick infestations, and to cause reduced tick survival and degeneration of gut and salivary gland tissues. In this research, we extended these studies by testing whether targeting subolesin by RNAi or vaccination interfered with the ability of ticks to become infected with two tick-borne pathogens, Anaplasma marginale which causes bovine anaplasmosis and Anaplasma phagocytophilum, the causative agent of human granulocytin anaplasmosis. For the A. marginale studies, Dermacentor variabilis males were injected with subolesin dsRNA or saline and then were allowed to feed on cattle with ascending rickettsemias, while for the A. phagocytophilum studies, mice were immunized with the recombinant subolesin protein, infected with the pathogen and then infested with larval Ixodes scapularis. Tick infections were determined by quantitative polymerase chain reaction of gut and salivary gland tissues. In both experimental approaches, tick infections were significantly reduced. These results suggest that subolesin appears to be a candidate vaccine antigen that may contribute to control of multiple tick species and the reduction of tick-borne pathogens.
In Huila Province of Angola, 3864 ticks were collected during a parasitological survey carried out in the rainy season from October 1990 to April 1991. The samples were collected from cattle gathered for the annual vaccination campaign against contagious bovine pleuropneumonia, anthrax and blackleg in 18 veterinary stations of six municipalities. After tick classification, the following proportions of ticks were obtained: Rhipicephalus evertsi mimeticus (27.1%), Amblyomma pomposum (26.4%), Boophilus decoloratus (19.0%), Rhipicephalus zambesiensis (9.4%), Rhipicephalus duttoni (8.3%), Hyalomma marginatum rufipes (3.8%), Hyalomma truncatum (3.0%), Rhipicephalus punctatus (2.5%) and Ixodes cavipalpus, Rhipicephalus lunulatus, Rhipicephalus turanicus, Rhipicephalus evertsi evertsi, Rhipicephalus simus, each less than 1%. These ticks are well known in southern Africa as vectors of diseases caused by protozoa and rickettsiae (babesiosis, theileriosis, anaplasmosis and cowdriosis). Control programmes against ticks and tick-borne diseases should be based on critical studies regarding costs/risks/benefits in relation to socio-economic and ecological frameworks.
To examine in detail Borrelia burgdorferi strain diversity in the United States, 186 isolates from human, tick, and rodent sources were analyzed from multiple distinct geographic regions of the United States and abroad. Strains were characterized by genomic macrorestriction analysis and ospA and 23S rDNA gene sequencing followed by phylogenetic analysis. Results indicate that spirochetal isolates from the United States fall into two major divisions and nine or more subdivisions; human isolates fell into five of these subdivisions. Greater genetic diversity was observed among B. burgdorferi isolates from moderate climatic regions, consistent with increased tick vector and reservoir diversity. All of the Borrelia isolates were reactive by ospA polymerase chain reaction except for Borrelia hermsii controls and several tick isolates from the Northeast, which were shown to lack the 49-kb plasmid encoding outer surface protein A (OspA). The data suggest that US B. burgdorferi isolates demonstrate substantial genetic heterogeneity, with regional differences in spirochete populations.
A study was done at the USDA-ARS, Cattle Fever Tick Research Laboratory, Mission, Tex., to determine the efficacy of a 50% wettable powder (WP) amitraz formulation applied as a whole-body spray in a standard dip vat, and in a laboratory bioassay against Boophilus annulatus (Say) on cattle. A study also was done at the King Ranch in Kleberg County, Tex., to determine the stability of 50% WP amitraz in a dip vat under South Texas conditions Cattle were infested with all parasitic life stages of B. annulatus and were sprayed or dipped with a concentration of 0.025% amitraz. As determined by calculations of the index of reproduction, the whole-body spray treatment provided 86% control of the ticks and the dip treatment provided 99.8% control. Laboratory bioassay results compared favorably with those obtained with the dip vat treatment. Amitraz WP settled very rapidly in the freshly charged ranch vat. However, as more cattle were dipped and the vat became polluted with dirt and excrement, settling occurred much more slowly. Overall, amitraz remained stable in the vat during the test period.
Ticks and tick-borne diseases affect animal and human health worldwide and are the cause of significant economic losses. Approximately 10% of the currently known 867 tick species act as vectors of a broad range of pathogens of domestic animals and humans and are also responsible for damage directly due to their feeding behaviour. The most important tick species and the effects they cause are listed. The impact on the global economy is considered to be high and although some estimates are given, there is a lack of reliable data. The impact of ticks and tick-borne diseases on animal production and public health and their control are discussed.
OBJECTIVES: Apparent a frigore facial palsy could possibly mask manifestations of unrecognized Lyme's disease. Since commonly used corticosteroid treatment could be deleterious if Borrelia burgdorferi infection was indeed the cause, we conducted a prospective study to search for possible infections in cases of recently diagnosed a frigore facial palsy. METHODS: For 3 years, 1990-1992, 49 French centres diagnosed a facial palsy in 346 patients (310 adults, 36 children under 15 years of age; mean age 38; range 16 months to 83 years). The patients were divided into three groups: a) facial palsy alone, b) zoster origin recognized due to outer ear eruption and c) cases with meningoradiculitis or joint signs or cases with facial diplegia. A questionnaire was used to evaluate exposure to risk of tick bits. A control group was established with 246 serum samples from subjects matched with the patients for age, geographical origin and exposure to risk of tick bits. Laboratory tests (indirect immunofluorescence and Western blot) were performed to search for anti-Borrelia burgdorferi antibodies in serum samples, and cerebral spinal fluid when possible, collected at presentation, on day 30 and on day 90. RESULTS: Sixty percent of the patients were urban dwellers, 15% lived in rural and 25% in semi-rural areas. There were 294 patients with facial palsy alone and their serum results were compared with those of the matched controls. There was no significant difference in the positivity for Borrelia burgdorferi antibodies between these two groups. CONCLUSION: These findings indicate that, unless there are clinical signs suggestive of borreliosis, it would not be necessary to test for Lyme's disease in patients with apparent a frigore facial palsy.
Effects of fetal bovine serum (FBS) and complement on phagocytic activity in Ornithodaros moubata (Murray 1877) hemocytes and protease activity in the hemocytes were examined. At least three morphologically different cell types, granulocytes, plasmatocytes, and prohemocytes, were detected in hemolymph of O. moubata, and granulocytes and plasmatocytes showed phagocytic activity. FBS altered phagocytic activity of granulocytes, and complement affected phagocytic activity of plasmatocytes. Ticks were inoculated with fluorescent polystyrene beads in combination with FBS or complement. The average number of beads in granulocytes was significantly higher in the FBS injected group than the control (P < 0.01). The percentage of bead-ingesting plasmatocytes in complement inoculated ticks was significantly lower than that in heat-inactivated complement inoculated and control ticks (P < 0.05). Proteases of tick hemocytes localized in small granules in the cytoplasm not only in phagocytic hemocytes but also in prohemocytes. Results suggested modulation of tick hemocyte function through serum components, and digestion of phagocytosed foreign bodies in the hemocytes.
Over 500 cattle of all age groups on 2 farms in Zimbabwe were immunised against theileriosis using the "infection and treatment" method and disease prevalence and their productivity assessed during a period of 18 months. The immunising stock, Theileria parva (Boleni) was isolated in Zimbabwe. None of the immunised cattle suffered from theileriosis upon natural exposure whereas 22 unimmunised cattle died of theileriosis and a further 48 required treatment for theileriosis. In the first year, some immunised cattle were maintained with minimal threshold dipping (once or twice during the rainy season). During periods of very high tick challenge of 100 to 1,000 Rhipicephalus appendiculatus per animal from January to March, a transient decrease in liveweight gain was observed particularly in cows. However, by the end of the period of observation, the weights had recovered so that intensively dipped and immunised and threshold or strategically dipped groups of cattle showed no significant differences. From the results it was estimated that each engorging female R. appendiculatus caused a temporary depression in weight gain of 8 grams. In young stock the weight loss was exacerbated by the presence of screw worm (Chrysomya bezziana) infestation. It was then possible to define an economically attractive integrated tick and theileriosis control strategy based on these findings, whereby immunised cattle were dipped 6 times between mid-December and mid-March. In this regimen, no weight loss occurred and no cases of screw worm were observed. For each of 3 herd sizes of 250, 500 and 1,000 cattle, comparisons were made of the costs of 4 different control options: (i) Intensive dipping (40 times/year) (ii) Intensive pour-on acaricide treatments (18 times/year) (iii) Theileria immunisation with strategic dipping (6 times/year) (iv) Theileria immunisation with pour-on treatment (4 times/year) It is concluded from these studies that, on farms where theileriosis is a serious problem, immunisation coupled with a strategic dipping programme is economically very attractive. In the year in which immunisation is carried out, costs will be higher than for intensive dipping, but from the second year on, the costs are decreased to approximately 50% of those for intensive dipping.
The Ixodes scapularis Genome Project (IGP), the first to sequence a tick genome, will provide an unparalleled resource for studying tick biology and tick-host-pathogen relationships, and identifying novel targets for tick and tick-borne disease control. The IGP will be the first genomic analysis of a member of the subphylum Chelicerata and will accelerate the pace of tick research. The challenge for scientists is to translate IGP data into public health benefits.
The ability of hard ticks to prevent infection by bacteria was investigated. During a 72-h period, virtually all Dermacentor variabilis females survived inoculation with Bacillus subtilis, Escherichia coli, and Staphyloccocus aureus but few survived infection with Pseudomonas aeruginosa. The hemocyte population increased to peak abundance at 48 h to approximately 6 times that of the uninfected controls. In contrast, the soluble hemolymph protein content decreased inversely as the hemocytes increased. D. variabilis hemolymph was found to be constitutively antimicrobial (i.e., hemolymph from bacteria-naive individuals inhibited bacterial growth). Infection with various bacterial species enhanced this innate capability. When hemolymph fractions separated by high-pressure liquid chromatography were tested for their ability to inhibit microbial growth, activity against the gram-positive bacterium, B. subtilis, was found in 2 polar fractions. Antimicrobial activity was lost when the fractions were incubated with protease. The least polar fraction contained 1 major protein, M(r) 14.5 kDa, that comigrated with human lysozyme. This protein, tentatively identified as tick lysozyme, was abundant in bacteria-naive ticks but increased greatly (43%) following challenge with B. subtilis. The identity of the other, more polar protein is unknown. Studies to characterize these antimicrobial proteins are planned.
Tick saliva (or salivary gland extract) potentiates the transmission of Thogoto (THO) virus to uninfected ticks feeding on a non-viraemic guinea-pig. This phenomenon has been named saliva activated transmission (SAT). To investigate the potential of different haematophagous arthropods to mediate SAT, guinea-pigs were infested with uninfected R.appendiculatus Neumann nymphs and inoculated with THO virus and salivary gland extract (SGE) derived from a range of ixodid (metastriate and prostriate) or argasid ticks, or mosquitoes; control guinea-pigs were inoculated with virus alone. Enhancement of THO virus transmission was observed only when SGE was derived from metastriate ticks. Comparison with the vector potential of these various arthropod species revealed that enhancement of THO virus transmission was specific for ticks which were competent vectors of the virus. The data indicate a correlation between vector competence and the ability of haematophagous arthropods to mediate SAT of THO virus.